1. Field of the Invention
Provided are computer readable recording media, system, and method for using wired endpoints to determine position information for wireless endpoints in a network
2. Description of the Related Art
Portable information communication endpoints such as mobile phones, smart phones, tablet PCs, and notebook PCs have proliferated, and many people now carry these information communication endpoints with them at all times. These information communication endpoints incorporate a Global Positioning System (GPS) function, and a number of services are provided using position information acquired using this GPS function. These services include the display of a map including a user's current location, as well as services directing a user to a desired location.
A technology is known in which the position information of a mobile endpoint is acquired on the basis of base station cell information and information obtained from GPS, and the position information is registered in a server using a long-distance wireless network such as Wideband Code Division Multiple Access (W CDMA), Personal Digital Cellular (PDC), or CDMA2000. However, the utilization cost of this technology is high, and indoor position measurements cannot be performed using GPS. It is also difficult to perform a position measurement that takes into account such factors as an office layout. Therefore, a technology is desired that can perform an indoor position measurement easily and inexpensively, and that can perform a position measurement while taking into account such factors as an office layout.
In recent years, wireless local area networks (LAN), which are one type of short-range wireless communication system, have become more widely used in the market. A technology has been proposed which uses a wireless LAN to easily and inexpensively acquire the position of an information communication endpoint.
A technology has also been proposed in which positioning access points are installed to improve the detection accuracy of position information using the strength of wireless LAN. In this technology, wireless LAN access points functioning only as position identifying infrastructure are installed in an indoor space where GPS cannot be used, and these wireless LAN access points only perform beacon transmissions required for positioning. By narrowing and refining the radio wave areas, detection accuracy can be improved at low cost.
A technology has also been proposed in which packets carrying position information from a known endpoint are transmitted in ad hoc mode as beacon packets over an ad hoc network, and the position of the endpoint is estimated, for example, from the number of hops it takes for the position information to reach the receiving mobile node. In this technology, an endpoint that has acquired its absolute position using GPS broadcasts its own position information to nearby endpoints, and an endpoint estimating its own position range estimates its own position range using the broadcast information and the number of hops from GPS to itself as parameters.
One technology that estimates distance using known radio waves is called the Received Signal Strength Indication (RSSI) method. In this method, the relationship between distance and field intensity attenuation is used to estimate the distance to a radio wave generating node from the field intensity of the radio waves received by an object estimating the distance (end point). This technology will now be explained with reference to FIG. 1.
In FIG. 1, a notebook computer PC1 serving as the end point is at coordinates representing a three-dimensional position (xEst, yEst, zEst), and four notebook computers PC2, PC3, PC4, PC5 generating radio waves near notebook computer PC1 are at coordinates (x1, y1, z1), (x2,y2,z2), (x3,y3,z3), and (x4,y4,z4), respectively. The distance of each notebook to notebook computer PC1 is r1, r2, r3, r4, respectively.
The actual field intensity from each of the notebook computers PC2-5 is measured by notebook computer PC1, and values p1, p2, p3, p4 are obtained. When this is expressed in relationship to distance, the diagram shown in FIG. 2 is obtained. FIG. 2 shows that field intensity is inversely proportional to distance.
In this method, the distance between the end point and a plurality of nodes is estimated, and, using the distances and the position information of each node, the three-dimensional position coordinates (xEst, yEst, zEst) of the end point can be calculated using the following system of equations.
                    {                                                                                                                        (                                                                        x                          Est                                                -                                                  x                          1                                                                    )                                        2                                    +                                                            (                                                                        y                          Est                                                -                                                  y                          1                                                                    )                                        2                                    +                                                            (                                                                        z                          Est                                                -                                                  z                          1                                                                    )                                        2                                                  =                                  r                  1                  2                                                                                                                                                                    (                                                                        x                          Est                                                -                                                  x                          2                                                                    )                                        2                                    +                                                            (                                                                        y                          Est                                                -                                                  y                          2                                                                    )                                        2                                    +                                                            (                                                                        z                          Est                                                -                                                  z                          2                                                                    )                                        2                                                  =                                  r                  2                  2                                                                                                                                                                    (                                                                        x                          Est                                                -                                                  x                          3                                                                    )                                        3                                    +                                                            (                                                                        y                          Est                                                -                                                  y                          3                                                                    )                                        2                                    +                                                            (                                                                        z                          Est                                                -                                                  z                          3                                                                    )                                        2                                                  =                                  r                  3                  2                                                                                                                                                                    (                                                                        x                          Est                                                -                                                  x                          4                                                                    )                                        4                                    +                                                            (                                                                        y                          Est                                                -                                                  y                          4                                                                    )                                        2                                    +                                                            (                                                                        z                          Est                                                -                                                  z                          4                                                                    )                                        2                                                  =                                  r                  4                  2                                                                                        Equation        ⁢                                  ⁢        1            
Another such technology is called the Time Difference of Arrival (TDoA) method. In this method, the time difference between a radio wave transmission time of a node generating radio waves and a radio wave reception time of an end point is measured, and the distance between them is calculated from the time difference and the transmission speed of the radio waves.
In the configuration shown in FIG. 1, time differences t1, t2, t3, t4 are determined from the times at which radio waves were transmitted from notebook computers PC2-5 and the times at which the radio waves were received by notebook computer PC1. When this is expressed in relationship to distance, the diagram shown in FIG. 3 is obtained. FIG. 3 shows that the time difference is proportional to distance.
In this method as well, the distance between the end point and a plurality of nodes is estimated, and, using the distances and the position information of each node, the three-dimensional position coordinates (xEst, yEst, zEst) of the end point can be calculated using the system of equations in Equation 1.